A type of modern blowout preventer (“BOP”) contains large metal blocks, ram blocks, that move to contact tubulars or other objects in the wellbore and shear, cut or break them into two pieces that are no longer contiguous. Some of these blowout preventers only shear tubulars without forming a seal in the wellbore, while other BOPs are designed to shear and seal the wellbore so that no flow of fluid or gas passes through the ram blocks, and hence the BOP. Stopping wellbore flow is the task of a shear-and-seal BOP, the last line of defense in uncontrolled wellbore pressure events.
In a shearing operation, the ram blocks may be required to remain in the close position—the position of stopping all flow through the wellbore—indefinitely. The ram blocks are pushed together in this situation and are held in place in this close position indefinitely. Mechanical locking mechanisms function to hold shear ram blocks in place until wellbore pressure has been controlled by other means. These two functions, shearing tubulars and subsequently retaining that close position to stop flow indefinitely, have presented significant challenges to the oil and gas industry.